This project is designed to investigate associations between impulsivity and sensitivity to drug reward. Impulsivity and sensitivity to the rewarding effects of drugs are two known risk factors for drug abuse. Impulsivity is thought to have a causal role in the onset of abuse. It is a multi-faceted construct comprised of impulsive action (difficulty controlling behavior); impulsive choice (difficulty delaying gratification); impulsive attention (difficulty focusing on the task at hand); and impulsive personality (predisposition to rash action). Sensitivity to reward is also thought to influence susceptibility to use drugs, although arguments have been made that risk is related to both higher than average or lower than average sensitivity to reward. The relationship between impulsivity and reward sensitivity is poorly understood. The two constructs may independently contribute to risk for drug abuse, or they could be related to each other. There is some evidence that high impulsivity is related to low reward sensitivity, especially sensitivity to the rewarding effects of drugs. Additionally, thee is neurobiological evidence linking both impulsivity and drug reward to dopamine activity, further suggesting that the two might be related. The aim of the current proposal is to examine sensitivity to the subjective rewarding effects of the stimulant drugs amphetamine (0-20 mg), MDMA (0-1.5 mg/kg), and caffeine (0-200 mg) in individuals high and low on each of the sub-components of impulsivity. It is hypothesized that highly impulsive individuals will exhibit a dampened subjective response compared to non-impulsive individuals. Additionally, the proposal will test if this dampened response to reward is also observable in response to sweet taste liking, a measure of non-drug reward, or if it is specific to drugs of abuse.